diff: teach --stat to ignore uninteresting modifications

When options such as --ignore-space-change are in use, files with
modifications can have no interesting textual changes worth showing.  In
such cases, "git diff --stat" shows 0 lines of additions and deletions.
Teach "git diff --stat" not to show such a path in its output, which
would be more natural.

However, we don't want to prevent the display  of all files that have 0
effective diffs since they could be the result of a rename, permission
change, or other similar operation that may still be of interest so we
special case additions and deletions as they are always interesting.

Signed-off-by: Matthew Rogers <mattr94@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 36 insertions, 2 deletions

diff --git a/t/t4015-diff-whitespace.sh b/t/t4015-diff-whitespace.sh
index 88d3026..8bdaa0a 100755
--- a/t/t4015-diff-whitespace.sh
+++ b/t/t4015-diff-whitespace.sh
@@ -789,7 +789,7 @@ test_expect_success 'checkdiff allows new blank lines' '
 	git diff --check
 '
 
-test_expect_success 'whitespace-only changes not reported' '
+test_expect_success 'whitespace-only changes not reported (diff)' '
 	git reset --hard &&
 	echo >x "hello world" &&
 	git add x &&
@@ -799,10 +799,44 @@ test_expect_success 'whitespace-only changes not reported' '
 	test_must_be_empty actual
 '
 
-test_expect_success 'whitespace-only changes reported across renames' '
+test_expect_success 'whitespace-only changes not reported (diffstat)' '
+	# reuse state from previous test
+	git diff --stat -b >actual &&
+	test_must_be_empty actual
+'
+
+test_expect_success 'whitespace changes with modification reported (diffstat)' '
+	git reset --hard &&
+	echo >x "hello  world" &&
+	git update-index --chmod=+x x &&
+	git diff --stat --cached -b >actual &&
+	cat <<-EOF >expect &&
+	 x | 0
+	 1 file changed, 0 insertions(+), 0 deletions(-)
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'whitespace-only changes reported across renames (diffstat)' '
 	git reset --hard &&
 	for i in 1 2 3 4 5 6 7 8 9; do echo "$i$i$i$i$i$i"; done >x &&
 	git add x &&
+	git commit -m "base" &&
+	sed -e "5s/^/ /" x >z &&
+	git rm x &&
+	git add z &&
+	git diff -w -M --cached --stat >actual &&
+	cat <<-EOF >expect &&
+	 x => z | 0
+	 1 file changed, 0 insertions(+), 0 deletions(-)
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'whitespace-only changes reported across renames' '
+	git reset --hard HEAD~1 &&
+	for i in 1 2 3 4 5 6 7 8 9; do echo "$i$i$i$i$i$i"; done >x &&
+	git add x &&
 	hash_x=$(git hash-object x) &&
 	before=$(git rev-parse --short "$hash_x") &&
 	git commit -m "base" &&